Question

Why do most transcripts begin with an adenosine rather than one of the other ribonucleotides? Which nucleotide is the second most common at the beginning of transcripts?

Answer 1

Ans. Because RNA polymerase does not require primer to transcribe DNA to RNA. Hence, RNA polymerase needs a base pair that will form a weak bond, and the A:U base pair in RNA is the weakest. Weak bond between Adenine: Uracil lower the destabilization energy of DNA-RNA duplex and also helps in dissociation from RNA polymerase. Uracil nucleotide is the second most common nucleotide at the beginning of transcripts. Because first codon ( triplet of codon) in transcripts is the start codon i.e, AUG.